Automobile theft in the United States and in other countries constitutes a serious problem. The number of automobiles stolen, whether for simple "joy riding" or criminal intent to permanently deprive the owner of the use of the automobile, is substantial. In addition to the significant losses to automobile owners and automobile insurers, stolen automobiles frequently are driven in a dangerous manner creating significant risk to other drivers in the vicinity of such a stolen automobile.
In an effort to reduce the number of vehicles which are stolen, some theft protection devices have been incorporated into automobiles by manufactures for some time. Most automobiles have a steering lock which is engaged when the ignition switch is turned to its "off" position and the ignition key is removed from the vehicle. Usually this is a mechanical lock; and it is effective to prevent the automobile from being driven away, even if the ignition system is "jumpered" to permit starting of the engine. Steering wheel lock systems, however, can be broken relatively easily; and if they are broken, they are costly to replace or repair.
Most modern automobiles also have a buzzer or gong-type of alarm system which is sounded any time the driver's door of the vehicle is opened when the ignition key is left in the ignition lock after the engine has been turned off. The use of this type of alarm lessens the possibility that the driver will leave the vehicle with the key in the ignition lock. As a result, if the ignition key has been removed, it generally is necessary for a thief to "jumper" or "hot-wire" the vehicle ignition system in order to start the vehicle. For a skilled thief, however, the time required to do this is relatively short (usually less than 45 seconds); so that removal of the key is not a particularly great deterrent for an experienced car thief.
Another approach to minimizing the possibility of the theft of an automobile is to install a siren type of audible alarm system in the vehicle. This alarm is activated any time the door (or hood) of the vehicle is opened without first deactivating the alarm. Generally, alarms of this type are activated and deactivated by a separate key or computer key pad control. If the vehicle door is opened without first deactivating a previously activated alarm, a loud audible alarm is sounded to call attention to the vehicle of residents or passersby in the vicinity of the vehicle. Because of the extremely loud noise which such alarms generate, a potential thief generally will leave the vicinity of the vehicle immediately after the alarm is set off. Alarms of this type, however, are relatively expensive to install and constitute an additional nuisance, inasmuch as they must be separately activated by the vehicle owner or driver each time the vehicle is parked and then must be deactivated by means of a separate action each time the owner wishes to drive the vehicle. Because of these additional steps, vehicle owners frequently forget to activate the alarm or purposely neglect to activate the alarm if the vehicle is to be parked in a location for a relatively short period of time. In view of the fact that a thief usually can get a motor vehicle started and underway within 45 seconds, the practice of leaving a vehicle alarm turned off for even short time intervals completely defeats the purpose for which the alarm originally was installed.
A different approach to theft prevention which exists in the prior art is to engage or lock the main brakes of a vehicle to maintain braking pressure on the vehicle brakes whenever the vehicle is stopped and the ignition is turned off. Such systems typically utilize a check valve in the brake system which functions to maintain the brake pressure when the ignition is off. In most of these systems, brake pressure must be applied to the brakes through the normal actuation of the brake pedal, prior to and during the turning off of the ignition switch, to cause fluid pressure to be applied through the check valve to the brakes. Upon release of the brake pedal, the check valve prevents fluid return to the master cylinder; and the brakes are held engaged. A variety of different techniques then may be employed to release the check valve so that normal operation of the vehicle may be resumed. Such release is automatically effected in some systems by turning on the ignition switch, while other systems employ additional switches or mechanisms which must be operated by the vehicle operator in conjunction with the turning on of the ignition switch before the brakes are released and operation of the vehicle may be resumed.
Typical patents of this general type are the patents to Cvetkovich #3,653,730; Whittemore #3,617,663; and Noguchi #3,322,246.
In all of the prior art brake locking systems known to applicant, it is necessary for the driver to take some type of positive action to insure that the brakes are locked once the ignition is turned off and the key is removed. In many of the prior art systems, this involves the application of pressure through the brake pedal itself. In some systems, some other mechanisms must be operated. In all of these systems, however, it is possible to stop the vehicle turn it off and remove the ignition key without engaging the brake locking system. As a consequence, unless the vehicle operator goes through such a separate step, comparable to the activation of the audible alarms discussed above, the vehicle frequently is left unattended without the brakes being locked. In such an event, a potential thief has no more difficulty in stealing such a brake-lock equipped vehicle than he has for a conventional vehicle without such a system in it.
Brake lock systems, of the types described in the above identified patents, however, appear to be a desirable approach to theft prevention, provided they are utilized each time the vehicle is left unattended. A secondary advantage of such brake lock system is that the additional safety of preventing an unattended vehicle from rolling is automatically attained as part of the theft prevention feature. For example, if a vehicle is parked on a hill, the application of an anti-theft brake locking system also functions to prevent the vehicle from accidentially rolling down the hill, since it is incapable of doing this so long as the brakes remain applied.
It is desirable to provide an improved fully-automatic, vehicle hydraulic brake-locking system which overcomes the disadvantages of the prior art systems and which is relatively inexpensive, easy to install, and is as effective and fool-proof as possible to significantly minimize the potential for theft of a vehicle on which the system is installed.